This invention relates to a swaybrace system which automatically applies and maintains a desired predetermined preload condition on a store (a bomb, rocket, fuel tank, etc.) suspended on an airborne ejector rack to hold the store securely while at the same time limiting the amount of load which is induced on the ejector rack hook which must be overcome during the act of store release. For example, in any given installation of a store on an ejector rack, the store must be held securely by lateral restraints, commonly swaybrace arms, to prevent store yaw and roll excursions which might induce aircraft wing/pylon vibrations and thus fatigue the aircraft structure and result in airframe in-flight failure. In addition, it is necessary to prevent store oscillations when considering such stores as rocket pods or bombs, since undue motion of the pods or bombs during a firing or ejection would disturb the aim of the rocket or bomb. Further, the mechanism which applies the store restraints must not, in executing its function, induce such reactive loads in the ejector rack between the rack hook and store lug, that the hook is prevented from opening to release the store when commanded to do so. Finally, it is advantageous that the application of the lateral restraints to the store during the act of store loading be automatic so that loading time and ground crew tasks are minimized.
In the prior art, the methods of accomplishing the above noted functions have included purely manually emplaced lateral restraints, and automatically applied restraints with limited capabilities. In the former, the lateral restraints consist of pairs of swaybrace arms integral with the ejector rack (or pylon or aircraft directly) near the fore and aft ends. These arms accommodate varying size stores by virtue of bolt-on loadbearing pads on the ends of the swaybrace arms. These pads are manually torqued down onto a suspended store to make hard contact. The amount of force exerted on the store by the pads is governed by the bolt torque applied. It is time-consuming, and not always an easy task, to apply the exact correct torque to properly restrain the store but limited to prevent hook and lug lockup.
Automatic self-adjusting swaybrace systems have embodied various mechanisms consisting of cams, wedges or like devices which function to bias the swaybrace arms down to make contact with the store surface itself through pads on the arms or pads emplaced on the store surface. These mechanisms in some instances force contact of the restraining swaybrace arms as a gap develops under one swaybrace arm due to store rolling motion in a direction opposite or away from that particular restraint. These automatic swaybrace systems can be grouped in two broad categories; those wherein the two arms of a pair, either fore or aft, are actuated independently, and are free to take up clearance independently, and those wherein the two arms of a pair are linked together so that one can take up clearance only if the other can also move. For those which act independently, excessive pre-load can develop, because as a store rolls from side to side relative to the rack creating a gap between it and the swaybrace arm pads, the arms take up the gap successively until large loads are developed at the pads. These loads are reacted by the rack hooks, which in turn are unable to open due to hook/lug friction. Swaybraces which act independently as a pair cannot take up any gap which arises as a result of store roll, since the heavily loaded swaybrace arm remains in contact with the store and prevents the opposite unloaded arm from dropping down to take up the clearance. This latter class of automatic swaybrace mechanism also cannot exert appreciable pre-load on a store, since it is limited by whatever spring force is available to actuate its wedges or cams. This force is usually quite small and well below the 1000 pound per arm pad pre-load order of magnitude which is required. Thus, this type mechanism cannot develop sufficient loads to deform thin skinned stores to the point where the skin contacts the internal structure, resulting in a very loosely restrained stores. Hence, one class of self-adjusting swaybrace system develops loads which are too large and prevent hook opening, while the other develops no appreciable pre-load so that stores hang too loosely and endanger aircraft flight or accurate store aiming.
The following patents represent prior art known to applicant pertaining to these and various other similar or more unrelated systems for restraining stores, namely: U.S. Pat. Nos. 1,528,942; 1,784,011; 2,010,511; 2,451,481; 2,461,406; 2,526,903; 2,552,578; 2,822,207; 2,889,746; 3,056,623; 3,500,716; 3,598,341; 3,670,620; 3,784,132; 3,840,201; 3,942,749; 3,967,528; 4,050,656; and British Pat. No. 440,156. None of these patents disclose or suggest the automatically self-adjusting and load-limiting swaybrace system of the present invention, to automatically obtain and automatically maintain a predetermined preload condition.